A UHF RFID transponder, sometimes called a “tag,” generally comprises an antenna, a matching circuit, an integrated circuit (IC), and a substrate. The antenna may be constructed from etched, vapor-deposited, chemically deposited, or electro-deposited copper or aluminum, or from conductive silver inks. The matching circuit may be integrated into the antenna design. The IC is electrically connected to the antenna, such as by a direct electrical connection or a capacitive connection. The substrate may be a PET polyester or paper. The transponder may be provided with a pressure-sensitive adhesive or the transponder may be integrated into a printable or printed label to facilitate application of the transponder to an object.
Transponder performance is degraded when the transponder is placed near metal, e.g., applied to a metal object. A spacer, which may be made of foam, may be interposed between the transponder and the conductive surface. The resulting separation mitigates the problem but does not eliminate it. Thus, the transponder continues to suffer from significant degradation in performance. In some instances, the transponder operates at approximately 1-3% efficiency.